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  Lining method and lining installation for the production of multi-layer productsUSPTO Application #: 20070039693Title: Lining method and lining installation for the production of multi-layer products Abstract: The invention relates to a lining method and a lining installation for the production of multi-layer products which are used, for example, to produce floor or wall coverings or interior trim for passenger transport vehicles, such as cars, railroad cars, ship cabins and aircraft cockpits. (end of abstract) Agent: Nath & Associates - Alexandria, VA, US Inventors: Luc Forget, Alexandre Siche USPTO Applicaton #: 20070039693 - Class: 156321000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070039693. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a doubling method as well as to a doubling equipment for manufacturing multilayer products, notably used for making floorings or wall claddings, as well as for the interior trim of vehicles used for person transportation, such as automobiles, railway wagons, ship cabins and aircraft cockpits. [0002] Multilayer products comprising a polymeric backing and a wear layer containing copolymer of the ionomer type are particularly targeted. [0003] For making floorings and wall claddings, as well as trims for passenger compartments of vehicles, sheet multilayer products are currently used, which comprise a backing layer or substrate and a wear surface layer. The backing layer generally has a decorative face onto which the wear layer is applied. The latter is used for protecting the decorative face of the substrate. It is usually transparent and should have adequate resistance to mechanical aggressions (impacts, abrasion) and to chemical aggressions under normal conditions of use. These functions of multilayer products condition the selection of the materials used for making them. This selection is further conditioned by sanitary, environmental and application considerations. In particular, the multilayer products should adapt to being applied by rolling or thermoforming which involves the use of thermoplastic polymers. Adherence of the superimposed layers should be sufficient for providing cohesion of the multilayer products in the applications for which it is intended. It is further desirable to select materials which allow recycling of the used multilayer products. Moreover, exudation of volatile materials (such as plasticizers) should be avoided or limited during the use of these multilayer products. [0004] Polyvinyl chloride (PVC) has been used for a long time for manufacturing sheet multilayer products intended for making carpets or wall claddings or trims for vehicle passenger compartments. However, considerations related to the protection of the environment argue for replacement of polyvinyl chloride with chlorine-free polymers or copolymers. Quite naturally, the selection was directed towards olefinic polymers and copolymers, especially polymers and copolymers of ethylene and propylene, given their relatively low price cost and their good chemical and thermal properties. [0005] A disadvantage of olefinic polymers in such applications lies in the difficulties encountered upon doubling the individual layers in order to form a multilayer product. Indeed, olefinic products badly lend themselves to rolling as the products tend to adhere to the rolling cylinders. [0006] The technique conventionally used in PVC floorings, i.e., a coating followed by gelation is not feasible in the case of olefinic and/or ionomer products. [0007] The invention is directed to creating a new technique for doubling sheets in order to obtain a multilayer product having sufficient adherence between the layers which make it up and a high quality surface aspect. [0008] Accordingly, the invention relates to a method for manufacturing multilayer products comprising, on a polymeric substrate, at least one wear thermoplastic polymer layer. The method is characterized by the following steps: [0009] preheating the backing, preferably at a temperature between 100 and 130.degree. C., [0010] cold application of the wear layer on the preheated backing, [0011] melting the wear layer on the backing, to ensure that it adheres with the backing, preferably at a temperature between 120.degree. C. and 180.degree. C., [0012] cooling the obtained product to bring it to a temperature closed to room temperature. [0013] By means of this method, it is possible to obtain a multilayer product with good physical and chemical properties, notably as regards internal cohesion, adherence of the layers which make it up, heat properties, mechanical resistance to wear and impacts, resistance to chemical aggressions and transparency of the wear surface layer. The thereby obtained product has a high quality surface aspect. [0014] One of the advantages of this method lies in the fact that the wear layer is coldly applied (not preheated--at room temperature) and it is not in contact with the rolling cylinders. The aspect problems of surfaces resulting from localized adherence on the rolling cylinder are thereby avoided. Instead of exerting the required pressure for joining and firmly attaching the backing and the wear layer by a rolling cylinder or any other comparable device, adherence of the wear layer is obtained by melting the latter, performed in an oven by blowing hot air on the upper surface of the product. In practice and for economical reasons, air is used as a gas, preferably preheated air at a temperature close to that prevailing inside the oven. For particular applications, the use of inert gases such as nitrogen or oxygen-depleted air may also be contemplated in order to minimize possible oxidization reactions. [0015] The wear layer is not preheated before it is applied onto the backing which itself is preheated. An advantage of applying the cold wear layer (at room temperature) is that its handling is easier since the wear layer is not softened by heat only up to the moment when it enters in contact with the preheated backing. In fact the wear layer is a sheet or a film which is applied onto the backing and is not a molten mass which is spread out on the backing. [0016] It is also important to note that the wear layer is melted in a controlled way only during the passing in the oven and not before contact with the backing. Consequently, the gas pressure applied on the surface of the wear layer does not risk generating surface defects appearing in the finished product. [0017] This method is particularly well suited for manufacturing multilayer products with a large width (.+-.4 m) comprising on a polymeric substrate, a polymeric wear layer of the ionomer or PO type. The products may further comprise between the substrate and the wear layer, an intermediate layer of an olefinic polymer containing a metallocene. [0018] The backing of the multilayer products has the function of being used as a mechanical backing. It may include a decorative imprint on one of its faces or on both of its faces. The imprint may also be made on the wear layer if the latter is transparent. The backing may also comprise a mineral filler. It essentially comprises a polymeric, generally olefinic compound. The polymeric compound may be an olefinic homopolymer or copolymer. [0019] Subsequently, for reasons of simplification, the expression "polymer" will equally designate a homopolymer or a copolymer. [0020] The olefinic polymer entering the composition of the backing of the products according to the invention may be selected from polymers of ethylene, propylene, and butylene. It may be a homopolymer or a copolymer, for example a copolymer of ethylene and propylene, or a copolymer of ethylene and butylene. Standard polyethylenes and/or metallocene polyethylenes are preferred. High density polyethylenes (HDPE), low density polyethylenes (LDPE), linear low density polyethylenes (LLDPE) and linear very low density polyethylenes (VLDPE) are particularly recommended. [0021] In the multilayer products, the olefinic polymer of the backing is advantageously free of ionic bonds. By the expression "free of ionic bonds", it is meant that the number of carboxylic acid groups in the polymer does not exceed 25% and is for example between 0 and 15%. [0022] The polymer of the backing may comprise mineral fillers intended to give it particular mechanical properties. Mineral fillers which may be used in the backing comprise calcium carbonate, magnesium carbonate, calcium sulfate, barium carbonate, barium sulfate, kaolin, pyrogenated silica, aluminum hydrate and expansed graphite. [0023] The wear layer has the function of protecting the backing against mechanical and chemical aggressions in the applications for which the multilayer products according to the invention are intended. It preferably comprises a polymer of the ionomer type. [0024] Polymers of the ionomer type for the wear layer are well known in the arts. These are copolymers with ionic bonds, comprising a hydrocarbon chain containing carboxylic acid side groups partially or totally neutralized by cations. The hydrocarbon chain is an olefinic, for example ethylenic chain. The carboxylic acid groups for example comprise ethylenically .alpha. and .beta.-unsaturated carboxylic acids and the cations may for example comprise metal cations or amine cations. Further information concerning the copolymers of the ionomer type is notably accessible in documents FR-A-1 430 478, U.S. Pat. No. 3,264,272 and U.S. Pat. No. 3,322,734 as well as in the article, "The structure and properties of ionomers"--W. J. Machnight and T/R Earnest Jr., published in Macromolecules Reviews, Vol. 16, pages 41-122 (1981). [0025] The optimum thickness of the wear layer depends on several parameters such as the material used for said wear layer and the applications for which the multilayer products are intended. In practice, good results are generally obtained with wear layers having a thickness of at least 30 .mu.m (preferably 60 .mu.m), thicknesses between 40 and 300 .mu.m being particularly advantageous. [0026] Alternatively, the wear layer may be coated with a surface layer of polyurethane in order to strengthen abrasive wear resistance. [0027] The wear layer may comprise one or more intermediate layers of an olefinic polymer containing a metallocene. This intermediate layer is fixed on the wear layer so that it is located between the backing and the wear layer in the finished product. Advantageously, this intermediate layer is transparent. [0028] Advantageously, the intermediate layer comprises an olefinic polymer which may equally be a homopolymer or a copolymer. Homopolymers are well suited. Homopolymers of ethylene are preferred and among the latter, low density polyethylenes (LDPE) are particularly recommended. Continue reading... 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